Anyone can help me to understand why GEE report this question? Here is my code:

    var table = ee.FeatureCollection("projects/ee-qsz/assets/boreal_id1");
    print('table', table);
    // 定义时间范围
    var startYear = 2003;
    var endYear = 2011;
    var months = ee.List.sequence(1, 12);
    var years = ee.List.sequence(startYear, endYear);
    // 导入MODIS的EVI数据集
    var collection = ee.ImageCollection('MODIS/MOD09GA_006_EVI')
      .filterDate('2003-01-01', '2011-12-31');
    var clippedCollection = collection.map(function(image){
      return image.clip(table);
    print('rawdata', clippedCollection);
    // 创建一个函数,用于计算每个月的均值
    var monthlyMean = function(year, month) {
      var startDate = ee.Date.fromYMD(year, month, 1);
      var endDate = startDate.advance(1, 'month');
      var monlyfirstImage = clippedCollection.filterDate(startDate, endDate).first();
      var monthlyImages = clippedCollection.filterDate(startDate, endDate)
        .copyProperties(monlyfirstImage, ["system:time_start"])
        .copyProperties(monlyfirstImage, ["system:time_end"]);
        .set('system:time_start', startDate.millis())
        .set('system:time_end', endDate.millis());
      return monthlyImages;
    // 按年月调用函数,创建月度EVI时间序列
    var months = ee.List.sequence(1,12);
    var monthlyEvi = ee.ImageCollection.fromImages(
      ee.List.sequence(2003, 2011).map(function(year){
        return months.map(function(month){
          var evi = monthlyMean(year, month);
          // 设置时间属性为每个月的第一天
          var startDate = ee.Date.fromYMD(year, month, 1);
          var evi2 = evi;
          return evi2.set('month', month);
    print('Monthly EVI', monthlyEvi);
    // 定义一个函数,将时间戳转换为可读日期格式
    var formatTime = function(image) {
      var startTime = ee.Date(image.get('system:time_start'));
      var formattedTime_start = startTime.format('YYYY-MM-dd');
      var image_month = image.date().get('month');
      var endTime = ee.Date(image.get('system:time_end'));
      var formattedTime_end = endTime.format('YYYY-MM-dd');
      var image1 = image.set('system:time_start', formattedTime_start);
      var image2 = image1.set('system:time_end', formattedTime_end);
      return image2;
    // 对每个图像应用 formatTime 函数
    var formattedEvi = monthlyEvi.map(formatTime);
    print('Formatted Monthly EVI', formattedEvi);
    var colorizedVis = {
      min: -1,
      max: 1,
      palette: [
        'ffffff', 'ce7e45', 'df923d', 'f1b555', 'fcd163', '99b718', '74a901',
        '66a000', '529400', '3e8601', '207401', '056201', '004c00', '023b01',
        '012e01', '011d01', '011301'
    Map.setCenter(-7.03125, 31.0529339857, 2);
    // Map.addLayer(formattedEvi, colorizedVis, 'Colorized');
    // 计算系数d
    var d = ee.Number(2).multiply(Math.PI).divide(12);
    // 预先计算cos和sin项
    var costerm = ee.List.sequence(0, 11).map(function(i){
      return (d.multiply(i)).cos(); 
    var sinterm = ee.List.sequence(0, 11).map(function(i){
      return (d.multiply(i)).sin(); 
    // 定义计算季节性指数 SI 的函数
    var calculateSI = function(year) {
      var myDate = ee.Date.fromYMD(year, 1, 1);
      // 获取该年份的EVl数据
      var eviYear = formattedEvi.filter(ee.Filter.calendarRange(year, year, 'year'));
      //print('Formatted yearly EVI',eviYear);
      // 计算季节性指数 SI
      var mx_col = []; 
      var my_col = [];
      for (var i = 0; i < 12; i++) {
        var month = i+1;
        var eviMonth = eviYear.filter(ee.Filter.eq('month', month)).first();
        var L = eviMonth.select('EVI');
        var mx_i = L.multiply(ee.Number(costerm.get(i)))
                .copyProperties(eviMonth, ["system:time_start"])
                .copyProperties(eviMonth, ["system:time_end"]);
        var my_i = L.multiply(ee.Number(sinterm.get(i)))
                .copyProperties(eviMonth, ["system:time_start"])
                .copyProperties(eviMonth, ["system:time_end"]);     
      mx_col = ee.ImageCollection(mx_col);
      my_col = ee.ImageCollection(my_col);
      var mx = ee.Image(mx_col.mean().copyProperties(eviYear.first(), ["system:time_start"]));
      var my = ee.Image(my_col.mean().copyProperties(eviYear.first(), ["system:time_start"]));
      var si =  mx.expression(
        'sqrt(mx * mx + my * my)',
        {mx: mx, my: my}
      return si.rename(['SI']).copyProperties(eviYear.first(), ["system:time_start"]);
      //return mx;
    var test = ee.Image(calculateSI(2008));
    print('test', test);
    //Map.addLayer(test.select('SI'), colorizedVis, 'test');
    // 计算每年的季节性指数 SI
    var siCollection = ee.ImageCollection.fromImages(years.map(function(year) {
      return calculateSI(year);
    print('si', siCollection);
    var Vis = {
      min: -1.0,
      max: 1.0,
    Map.addLayer(siCollection,Vis, 'siCollection');
    var exportArgs = Export.image.toDrive({
      image: test,
      description: 'SI_2008',
      scale: 500,
      region: table.geometry().bounds(),
      fileFormat: 'GeoTIFF',  
      fileNamePrefix: 'SI_2008'

I have tryed to return mx,my and si. When I return mx and add it to map, there are no errors, but when I return my or si, GEE reported this error (in function calculateSI, line 97).

Expected a homogeneous image collection, but an image with an incompatible band was encountered. Mismatched type for band 'EVI': Expected type: Float<-0.0, 0.0>. Actual type: Float<-0.49999999999999994, 0.49999999999999994>. Image ID: 1 This band might require an explicit cast.

  • I see no mx, my, or si return in your code. I copied and this script works without issue, so we can't reproduce your error. Please update the question and add the specific lines your code fails
    – aldo_tapia
    Jul 17, 2023 at 12:43
  • Hi aldo, thanks for your answer sincerely. I am sorry I didn't report specific line of the error. And I can now tell you that the mx, mx and si are in the function calculateSI, which in line 97. You didn't find error when you run the code because I return mx in calculateSI. And that's why I am confused, when I return si or my in the funciton, I get the error.
    – qingsong
    Jul 17, 2023 at 14:48
  • I guess maybe its a value error in the calculateion of my, but I can't find where it is now.
    – qingsong
    Jul 17, 2023 at 14:59

1 Answer 1


I think I solve the problem. The problem is here:

var my_i = L.multiply(ee.Number(sinterm.get(i)))
                .copyProperties(eviMonth, ["system:time_start"])
                .copyProperties(eviMonth, ["system:time_end"]);  

GEE can't identify the type of the image. So I added a line of code:

my_i = ee.Image(my_i).toFloat();

And then it works!

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